If nobody can speak for an institution, the institution is muted, like in Poland, said Moe Biller, American Postal Workers Union president who is one of the three told that they face charges under the act, which restricts federal employee participation in partisan politics.

Biller`s and two other AFL-CIO-affiliated unions each endorsed former Vice President Walter F. Mondale in his unsuccessful race against President Reagan last fall.

Each official was warned of the charges earlier this month by the U.S. Merit Systems Protection Board`s special counsel.

In a statement, the AFL-CIO Executive Council condemned the Reagan administration ``for attempting to silence free speech.``

Because Biller, Kenneth Blaylock, president of the American Federation of Government Employees, and Vincent Sombrotto of the National Association of Letter Carriers are on unpaid leave from their federal jobs, prosecuting them ``stretches the law far beyond all rational limits,`` the statement said.

``The Reagan administration`s misuse of the Hatch Act is merely the most recent example of its anti-union biases and its implacable hostility to the rights of unions and their members,`` said the statement, read in part by AFL- CIO President Lane Kirkland at a news conference.

The statement also reiterated labor`s long opposition to the act, calling it ``bad public policy because each citizen -- including each federal and postal employee -- should be encouraged to participate in public affairs.``